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2017.03.14    予聴会

2017.03.07    予聴会

2017.02.24(Fri, 10AM)    "TBA"  Dr. Silvina Pagola Aubin

2017.02.21    "Toward Unified Physics of Quasi-One-Dimensional Organic Superconductors: (TMTTF)2X in the Metallic State (X=Br)"  Dr. Woun Kang (Professor, Department of Physics, Ewha Womans University, Seoul)
(TMTTF)2X is the sulfur analog of the well-known quasi-one-dimensional (Q1D) organic superconductor (TMTSF)2X and precedes it in the development of organic metals. Although they are metallic at room temperature, they undergo transitions into various insulating states at low temperature.
While the insulating states deserved intensive study by themselves, efforts have been made to bring (TMTTF)2X to a metal at low temperature and to find superconductivity therein. Over a period of 14 years, superconductivity was confirmed in four members of (TMTTF)2X such as X=Br, PF6, AsF6, SbF6under relatively high pressure. On the other hand, a generic phase diagram has been proposed to assume that the physics of the selenium and sulfur series must be treated on an equal footing. In an effort to support this idea, there has been a number of attempts to verify if the metallic state of (TMTTF)2X has indeed the same ingredients as those of (TMTSF)2X, but without much success until recently. In this study, we chose (TMTTF)2Br for a practical reason and studied the angular dependent magnetoresistance (AMR) and the Hall effect under pressure. Two of the most representative properties of Q1D metals, three-dimensional AMR oscillations (including Lebed resonances, Danner-Chaikin oscillations, and the third angle effect) and field-induced spin-density-waves, were finally confirmed in (TMTTF)2X.

2017.02.14    文献紹介

2017.01.31    "μSR and DFT Study of Non-Magnetic Anion-Based Organic Superconductor λ-(BETS)2GaCl4"  Ms. Dita Puspita Sari (JRA, 理研仁科加速器研究センター岩崎先端中間子研究室)
The 3rd generation organic superconductor λ-(BETS)2GaCl4 is an attractive material with possibility of FFLO (Fulde-Ferrell-Larkin-Ovchinnikov) phase [1] by means a Cooper pairs with nonzero total momentum and a spatially non-uniform order parameter. Symmetry of the superconductivity and the mechanism are still controversial. In order to approach to the Cooper pairing symmetry in the superconducting (SC) state of λ-(BETS)2GaCl4, we carried out zero field (ZF) and transverse field (TF) μSR under the fields of 30 G and 60 G down to 0.3 K at RIKEN-RAL Muon Facility in the UK. From ZF- SR, a slight increase in the muon-spin relaxation rate was observed below Tc = 5 K indicating a signature of the appearance of an unconventional SC state. From TF- SR, the temperature dependence of the damping rate which directly relates to the SC penetration depth can be well described by a mixture of the s- and d- wave components showing a possibility that the Cooper pair symmetry is not so simple and the SC gap is not uniform in the wave space. The s- component may be dominant in this case.
By a density functional theory (DFT), we calculated fermi surface, density of state (DOS), and transfer integral of the metallic state in λ-(BETS)2GaCl4. The calculated transfer integral on BETS molecules of the lambda stacking showing a noticeable different result with previous Huckel tight binding method. The supporting calculation and SR measurement result will be presented.
[1] W. A. Cogniglio, et al., PRB 83. 224507 (2011).

2017.01.17    "TBA"  Dr. Silvina Pagola Aubin

2017.01.10    "Study of the Spin Dynamic in Me4P[Pd(dmit)2]2 by μSR"  Dr. Abdel Jawad Majed
A series of quasi two dimensional (Q2D) triangular magnets, β'-(Cation)[Pd(dmit)2]2 show a variety of magnetic ground states such as antiferromagnetic states, charge ordered states and quantum spin liquid states depending on the choice of monovalent cations. Field dependent μSR measurement of the spin liquid compound is found to be consistent with the one dimensional diffusive motion of the spin excitations which contrasts with the Q2D nature of the charge transport of the same compound. To put this results into perspective, we present μSR measurements from Me4P[Pd(dmit)2]2.

2017.01.10(2)    "Transport Study of the Mott Transitionin EtMe3P[Pd(dmit)2]2"  Dr. Abdel Jawad Majed
Scaling of the conductivity of the Mott transition has proven to be far more challenging on the insulating side than on the metal side. We present the isothermal pressure dependence of the conductivity, thermopower coefficient, Hall coefficient and charge mobility through the Mott transition in EtMe3P[Pd(dmit)2]2. We show that the carrier number on both side of the metal-insulating transition, can be scaled with the same critical exponent.

2016.12.20    四半期ミーティング2

2016.12.13    四半期ミーティング1

2016.12.06    文献紹介

2016.11.29    文献紹介

2016.11.24    "New Polymorphs of Known Charge Transfer Salts of Tetrathiafulvalene: Mechanochemical Synthesis, Crystal Structure Analysis from Powders and Band Gap from FT-IR Spectroscopy"  Dr. Silvina Pagola Aubin
My present research efforts are dedicated to studying supramolecular reactions between crystalline solids carried out by grinding the reactants as powders (mechanochemical syntheses). This process can offer alternative synthetic routes, occasionally yielding products (crystal structures or stoichiometries) not obtainable from solution chemistry [1]. Mechanochemical reactions are carried out avoiding or reducing the use of reaction solvents, thus affording economic advantages and reduced environmental pollution. Using the liquid assisted grinding (LAG) method [2], small quantities of a selected solvent are mixed together with the reactants ground, and this affords the control of the polymorph of the products obtained, although the solvent properties and mechanistic aspects leading to this effect remain to be fully understood. In this presentation, I will describe the LAG syntheses [3] leading to two polymorphs of tetrathiafulvalene-chloranil (the green [4] and the black forms); two polymorphs (ionic and "red") of tetrathiafulvalene-chloranilic acid (TTF-CAH2); and two polymorphs of tetrathiafulvalene bromanil (TTF-BA), as well as the present understanding of the solvent effect in these LAG syntheses. Moreover, mechanochemical reaction products are always powders. Whereas the crystal structures of some of the above materials are known, two others have been solved from their X-ray powder diffraction patterns using direct-space methods, and one remains to be solved. The software for this purpose, WinPSSP, is available at http://users.uoi.gr/nkourkou/winpssp, and it will be briefly described. Other solid state properties will be summarized: FT-IR as a function of the temperature for estimation of the band gap in these semiconductors, neutron powder diffraction, room temperature magnetic susceptibility and band structure calculations.
[1] A.V. Trask, W. Jones, Top Curr. Chem. 2005, 254, 41-70. [2] T. Friscic, J. Mater. Chem. 2010, 20, 7599-7605. [3] Saul H. Lapidus, Amit Naik, Alex Wixtrom, Nestor E. Massa, Vinh Ta Phuoc, Leire del Campo, Sebastien Lebegue, Janos G. Angyan, Tarek Abdel-Fattah, and Silvina Pagola, Crystal Growth & Design 2014, 14, 91-100. [4] M. Le Cointe, M. H. Lemee-Cailleau, H. Cailleau, B. Toudic, L. Toupet, G. Heger, F. Moussa, P. Schweiss, K. H. Kraft and N. Karl, Physical Review B 1995, 51, 3374-3386.

2016.11.08    "First-Principles Study of The Electronic Structure in Molecular Conductors with Hybrid Functional"  圓谷 貴夫博士(物質・材料研究機構)注!14:00スタート
Molecular conductors show a rich variety of ground states such as antiferromagnetic state, quantum spin liquid, superconductivity, charge ordering, spin-density wave ordering, spin-Peierls state, and so on.
Such a richness of properties originates from relatively large Coulomb interactions. Simple tight-binding models have been proposed for explaining these phenomena qualitatively, but quantitative evaluation of physical quantities and understanding of microscopic picture between different phases remain challenging. To obtain reliable picture of the electronic states by first-principles density functional theory (DFT) calculations, computational approaches that can be applicable for molecular systems with a reasonable cost are highly required.
We study the molecular conductors showing charge ordering and antiferromagnetic state, and apply the hybrid functional approach with Heyd-Scuseria-Ernzerhof functional [1]. The formalism enables us to improve the exchange correlation energy by mixing the non-local exact (Fock) exchange and (semi) local exchange energy functional used in conventional DFT approaches such as LDA or GGA. We will discuss systems such as quasi-one-dimensional (TMTTF)2X where X = PF6 and AsF6 [2], quasi-two-dimensional α-(BEDT-TTF)2I3 [3], and hydrogen bonded system &kappaa;-H/D3(Cat-EDT-TTF)2 [4].
[1] J. Heyd, G. E.124, 219906 (2006).
[2] D. Jerome, Science 252, 1509 (1991). A. Jacho et al, Phys. Rev. B 87, 155139 (2013).
[3] P. Lunkenheimer et al, Phys. Rev. B 91, 245132 (2015).
[4] T. Isono et al, Nature Comm. 4, 1344 (2013). T. Isono et al, Phys. Rev. Lett. 112, 177201 (2014).

2016.10.25    2016年度中間報告2

2016.10.18    "Real-Space Investigation of Intermolecular Energy Transfer Dynamics"  今田 裕協力研究員 (理研 Kim表面界面科学研究室)
Energy transfer is an essential dynamic process in naturally configured photosynthetic systems, and it has also been used in various artificially designed energy-harvesting devices. Diverse functions have been realized by different regulations of the energy dynamics, and the microscopic understanding and molecular-level control of the energy transfer are long-standing challenging targets. So far, optical spectroscopy has been used to investigate excitation dynamics, however, the spatial resolution of conventional optical spectroscopy is limited, and a large part of energy transfers on the nanoscale is still unknown.
In this work, we conducted a molecular-level investigation of energy transfers in molecular dimers consisting of a free-base phthalocyanine and magnesium phthalocyanine (H2Pc and MgPc) by absorption/emission spectroscopy using STM (Fig. 1a) [1,2]. As shown in Fig. 1b, a luminescence signal from H2Pc at 1.81 eV was detected while locally exciting a nearby MgPc with the tunneling current of STM, clearly indicating an energy transfer from MgPc to H2Pc. The mechanism of the energy transfer is proven to be resonance energy transfer (RET) because charge transfer is prohibited by the energy-level alignment at the MgPc-H2Pc heterojunction.
1. Imada, H.; Miwa, K.; Imai-Imada, M.; Kawahara, S.; Kimura, K.; Kim, Y. arXiv: 1609.02701 (2016).
2. Imada, H.; Miwa, K.; Imai-Imada, M.; Kawahara, S.; Kimura, K.; Kim, Y. Nature doi: 10.1038/nature19765.

2016.10.11    2016年度中間報告1

2016.10.04    文献紹介(藤山、大島、川椙、磯野)

2016.09.27    文献紹介(加藤、崔、佐藤、李、金)

2016.09.06    予聴会(物理学会9/13-16)  

2016.09.01    予聴会(物理学会9/13-16)  

2016.08.02    "Spin-Lattice Decoupling in a Quantum Spin-Liquid Candidate, κ-(BEDT-TTF)2Cu2(CN)3"  磯野 貴之
A quantum spin liquid (QSL) is an exotic ground state of magnetic materials where strongly interacting electron spins do not order even at sufficiently low temperatures. A characteristic feature of the QSL is the presence of unique magnetic excitations, called spinons. In the titled QSL candidate, the nature of the magnetic excitation has been vigorously studied, for instance by the specific heat and thermal conductivity, but is highly controversial. In this talk, I will present our recent results of magnetocaloric-effect measurements on the titled material, which unveil anomalous spin-lattice relaxation in the QSL state. At very low temperatures, the thermal relaxation time between electron-spin and lattice systems rapidly increases, indicating that the spin system is decoupled from the phonon bath. This result may be understood by a spinon-pairing state or an algebraic spin-liquid state, where a small spinon density of states results in significantly weak spinon-phonon interactions.

2016.07.05    文献紹介

2016.06.28    "Recent Development in X[Pd(dmit)2]2 System"  伊藤 哲明博士(東京理科大学 理学部応用物理学科 伊藤研究室 准教授)
(1) Electronic Griffiths phase realized in EtMe3Sb[Pd(dmit)2]2
We have a consensus that the Mott transition is generally of the first order at low temperatures and a crossover at high temperatures in the pressure-temperature phase diagram. In contrast to this common understanding, EtMe3Sb[Pd(dmit)2]2 does not show a first order Mott transition under pressure. Instead, extremely slow fluctuations of electrons are observed around the Mott transition region. This unconventional Mott transition may be an analogous phenomenon to the slowly fluctuating spin phase, or Griffiths phase, realized in Ising spin systems with disordered lattices.
(2) Superconductivity in EtMe3P[Pd(dmit)2]2
The pairing symmetries of superconductivities realized in correlated electron systems are generally non-s wave. In this situation, the simplest form is d-wave, which is believed to be realized in organic superconductors, high-Tc cupratus, and so on. However, the triangular lattice destabilizes this d-wave state, opening up possibilities for exotic superconductivities (such as chiral or triplet superconductivity). I will discuss the superconducting state realized in EtMe3P[Pd(dmit)2]2, which is a correlated electron system with a triangular lattice.

2016.06.21    "The Blocking Temperature Distribution in Ferritin Extracted from Magnetization Measurements"  李 泰勳

2016.06.14    "Magnetic Properties of Cubane-Type Molecule Magenet"  金 星賢

2016.06.07    経過報告会 その2

2016.05.31    経過報告会 その1

2016.05.17    "Measurement of Proton Radius from Hyperfine Splitting Energy in Muonic Hydrogen"  佐藤 将春

2016.05.10    文献紹介(大島、川椙、藤山)

2016.04.26    文献紹介(加藤先生、崔、佐藤)

2016.04.19    年間計画 その2

2016.04.12    年間計画 その1

2016.04.05    年度報告会 その2(川椙、佐藤、圓谷)